An image transferring device applicable to an electrophotographic copier or the like may be constructed as shown and described in any of Japanese Laid-Open Patent Publication (Kokai) Nos. 54-19451, 56-120546, and 56-57069 by way of example. A device disclosed in these Laid-Open Publications includes a hollow cylindrical transfer drum, a conductive sheet wrapped around the transfer drum, and a transfer charger accommodated in the hollow transfer drum. Specifically, the transfer drum is constituted by opposite circumferential edge portions and an axially extending portion which links the edge portions to each other, the other portion being removed. Wrapped around such a transfer drum, the conductive sheet entirely covers the removed portion of the drum and is made of Mylar or like material. The transfer charger is adapted to transfer a toner image from a photoconductive drum which adjoins the transfer drum to a paper sheet which is supported and guided by the conductive sheet.
A problem with the above-described type of prior art image transferring device is that, since the conductive sheet for supporting and guiding a paper sheet is relatively thin and flexible, it is caused to yield into the transfer drum when tension is applied to the paper sheet due to sliding resistance while the paper sheet is transported between the transfer drum and the photoconductive drum, narrow guide plates, and others. When the conductive sheet is cased to yield as stated, a toner image practically fails to be transferred in a central area of the paper sheet or is dislocated there. Especially, in the case that such a device is applied to a color copier which effects multiple image transfer, color components which constitute a single image in combination are brought out of register with each other resulting in an unattractive copy. This is because the current applied to the transfer charger differs from one color component to another, and, therefore, the coulomb force of the conductive sheet which electrostatically attracts a paper sheet differs each time, causing the position of a paper sheet to vary transfer by transfer (color by color) in the area where the conductive sheet yields.